Automotive heat exchangers, such as radiators, have historically been the parallel flow type, with a core consisting of plurality of flat, evenly spaced metal flow tubes running end to end from an inlet manifold tank to an outlet manifold tank. Corrugated cooling fins brazed crest to crest between the tubes dissipate heat from the engine coolant through the tube walls and to a forced air stream blown over the core. The ends of the tubes are brazed fluid tight through matching slots in a pair of parallel metal header plates, and the entire core is typically an aluminum alloy in current production. Increasingly, the manifold tanks consist of a molded plastic shell crimped to the header plates, and the tanks comprise two sides of a basically four sided shape. On the other two sides of the core, a pair of outermost tubes may be left unused or "dead", or a pair of simple metal stampings may border and protect the outermost tubes, brazed at their ends to the ends of the header plates. The radiator may be mounted to the vehicle with the inlet tank at the top (and outlet tank on the bottom), a so called down flow configuration, or with both tanks on the sides. Especially in the down flow configuration, it has been found useful to build a four sided frame around the core, in effect, with a pair of side channels that border the sides of the core, and the ends of which are fixed to the ends of the two tanks. The side channels can then be fixed to the vehicle body to mount the entire radiator. Typically, the side channels are stamped steel members.
Because of expansion with heating, the core, when confined within a substantially fixed four side frame, is subject to warping forces that can tend to bend it out its normal flat shape. Regardless of whether the core actually warps, its tendency to do so can strain the core tubes, especially near the four corners. Some of this tendency can be reduced by allowing one end of each channel to "float" or slide to an extent, by fixing it to the end of the tank through an elongated slot. This does not remove all the warping force, however, and the relatively rigid steel side channel is not as inherently able to resist those forces as efficiently a more resilient material, such as plastic, would be. However, existing steel side channel designs are not optimally designed to be simply replicated in plastic, in the way that a molded plastic shell can directly replace the stamped metal shell of a manifold tank or "water box" in a radiator.